Conservation Genetics

, Volume 8, Issue 5, pp 1061–1071 | Cite as

Inbreeding levels and prey abundance interact to determine fecundity in natural populations of two species of wolf spider

  • David H. Reed
  • Amy C. Nicholas
  • Gail E. Stratton
Original Paper


Long-term effective population size is expected, and has been shown, to correlate positively with various measures of population fitness. Here we examine the interacting effects of population size (as a surrogate for genetic factors) and prey consumption rates (as a surrogate for environmental quality) on fecundity in two sympatric species of wolf spider, Rabidosa punctulata and Rabidosa rabida. Population size was estimated in each of seven genetically isolated populations in each of 3 years using mark-recapture methods. Fecundity was estimated as the mean number of live offspring produced by ∼15 females sampled from each population of each species each year for 3 years. Prey consumption rates were estimated by sampling ∼300 spiders per population per year and assaying the proportion of spiders with prey. Larger populations have higher fecundity and more genetic diversity than smaller populations. Variation among populations in fecundity for a given year could be attributed most strongly to differences in population size, with variation in prey consumption rates and the interaction between population size and prey consumption playing smaller but still important roles. During the most stressful environmental conditions, the smallest populations of both species experienced disproportionately low-fecundity rates, more than doubling the estimated number of lethal equivalents during those years. The evidence presented in this paper for inbreeding-environment interactions at the population level and further evidence for a log-linear relationship between population size and fitness have important implications for conservation.


Extinction Fitness Genetic diversity Genetic stochasticity Population size Prey consumption Wolf spiders 



We would like to thank Allison Derrick, Christian Felton, Alex Teoh and Winter Williams for help collecting spiders. Bianca Lowe photographed and measured spiders for many of the heritability estimates. Paul Lago kindly identified mantispids for us. Martín Ramírez and an anonymous reviewer provided useful suggestions on a previous draft of this paper. We thank the University of Mississippi for providing funding for this research.


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • David H. Reed
    • 1
  • Amy C. Nicholas
    • 1
  • Gail E. Stratton
    • 1
  1. 1.Department of BiologyUniversity of MississippiUniversityUSA

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